This histomorphometry core has been in integral part of our SCOR program since its inception in 1987. In the present application, the core provides histomorphometric support for four of the five projects and for the feasibility project on assessment of 3-d structure. Over the course of the five years the core will prepare and analyze over 600 rat and mouse specimens and 200 human biopsies. Bone histomorphometry will be employed to characterize the skeletal phenotype of transgenic mice which lack the p53 tumor suppressor gene. Bone histomorphometry will be used extensively to explore the mechanism of the anabolic action of PTH and interaction between dietary calcium deficiency and PT administration. Bone histomorphometry will be employed to characterize the cellular and structural effects of parathyroidectomy in postmenopausal women with mild primary hyperparathyroidism. Bone histomorphometry will be used to explore the mechanism of the initial intense anabolic action of PTH in patients with osteoporosis. Structural variables, assessed by Micro-MRI, will be correlated with histomorphometric variables of both cancellous and cortical bone structure. This core will employ state of the art technology and will bring over 15 years of experience to the analysis of the samples and interpretation of the data.